On an IP network, packets are flowing from various types of transmission sources to various types of destinations. At a point where the flows of the packets (referred to as “flows” hereinafter) meet, a packet transmission device for controlling the traffic of the flows is disposed. The packet transmission device includes a multistage structure for containing lines in which a plurality of flows are aggregated.
FIG. 20 is a diagram for explaining an example in which lines are contained in a packet transmission device. As illustrated in FIG. 20, the packet transmission device contains user lines, virtual lines, and a physical line. The user lines are lines in which flows that individual users use are aggregated, the virtual lines are lines in which the user lines are aggregated in units of groups such as companies to which the users belong, and the physical line is a line in which the virtual lines are aggregated into a fiber cable that connects one group such as a company or the like to another.
The packet transmission device that includes the multistage structure for containing a plurality of lines in this way typically controls the output rate (referred to as “bandwidth” hereinafter) of packets output from individual lines. As a method for controlling the bandwidth, a token control technique in which a token value that is information used for determining whether or not the output of a packet is permitted is used is widely utilized.
FIG. 21 is a diagram for explaining an example of a token control operation. In addition, in FIG. 21, a horizontal axis indicates a time, and a vertical axis indicates a token value stored in a predetermined memory. A packet transmission device that performs a token control operation adds a predetermined token value with a predetermined period to a total token value that indicates the sum of token values (refer to (a) in FIG. 21). In addition, the packet transmission device subtracts a token value, which corresponds to an output packet, from the total token value in the memory in response to the output of the packet (refer to (b) in FIG. 21). In addition, when, at the time of adding of the predetermined token value to the total token value in the memory, the total token value subjected to the adding exceeds a predetermined upper limit value, the packet transmission device discards the excess of the total token value over the predetermined upper limit value (refer to (c) in FIG. 21). While repeating such an operation, the packet transmission device outputs the packets from the individual lines in response to the total token values in the memory, and hence controls the bandwidths.
In addition, when there are a plurality of queues, in which packets are stored, in each line, the packet transmission device sequentially selects a queue in accordance with a round robin (RR) method, and sequentially output a packet from the selected queue. In addition, the RR method is a method of the related art, which is used for selecting an object in order.
FIG. 22 is a diagram for explaining the output of a packet, which uses the RR method. In addition, the packet transmission device illustrated in FIG. 22 contains the user line, the virtual line, and the physical line, and includes a plurality of queues, in which packets are stored, in each line. In addition, the packet transmission device illustrated in FIG. 22 includes a shaper function used for controlling the bandwidth using the token control.
The packet transmission device sequentially selects, in the user line, a queue from among a plurality of queues from which packets can be output owing to the shaper function, and outputs a packet from the selected queue to the virtual line (refer to (a) in FIG. 22). In addition, the packet transmission device sequentially selects, in the virtual line, a queue from among a plurality of queues from which packets can be output owing to the shaper function, and outputs a packet from the selected queue to the physical line (refer to (b) in FIG. 22). In addition, the packet transmission device outputs a packet, received from the virtual line, to another device (refer to (c) in FIG. 22).
Examples of the related art include Japanese Laid-open Patent Publication Nos. 9-224036, 9-224038, 9-200214, and 9-8812.